1. Field of the Invention
This invention relates in general to variable capacity rotary vane compressors for air conditioning systems, particularly for vehicles, and in particular to improvements in a control valve for that type of compressor.
2. Description of the Prior Art
One type of automotive air conditioning compressor in use is a variable capacity vane compressor. In this type of compressor, a compression housing has a chamber that is oval in shape. A cylindrical rotor extends through the chamber. The rotor has radial vanes mounted to it which slide radially in slots formed in the rotor. Refrigerant at suction pressure enters the compression chamber, with the vanes compressing the refrigerant, which passes outward through a valve.
The compressor demand varies according to speed and atmosphere conditions. At highway speed, the demand is usually lower than while idling on a hot day. To vary the capacity, a rotary valve disk or plate mounts in front of the compression housing and in engagement with a shoulder on the compression housing. The valve plate has a slotted perimeter which will change the position of the opening from the intake chamber into the compression chamber depending upon the rotational position of the valve plate. The valve plate is rotatably carried in a rotary valve housing, also known as a rear side block. The particular rotational position of the valve plate will change the quantity of refrigerant introduced between the vanes for compression by changing the timing of the compression cycle.
An actuator will rotate the valve plate to selected positions depending upon the changes in the discharge pressure and the intake or suction pressure. In one type, such as shown in U.S. Pat. No. 5,145,327, the actuator member comprises radial projections mounted to the rear side of the rotary valve plate and located within chambers. Each projection serves as a piston. Variable fluid pressure is applied to both sides of each piston. Also, a spring will urge the plate to a minimum delivery position.
In another type of actuator, the rotary valve plate is rotated by a spool piston, such as shown in U.S. Pat. No. 4,838,740. The spool piston moves linearly transverse to the axis of the rotor. The spool piston has a pivot pin that engages the plate to cause it to rotate as the spool piston moves.
A control valve applies pressure to the actuator for controlling the position of the rotary valve plate in response to intake and discharge pressures. In one type, the control valve supplies a control pressure to one side of the actuator piston, the other side of the actuator piston being at intake pressure. The control valve includes a bellows which has a stem that engages a ball valve. The bellows is located in a portion of the suction chamber. A plunger or bias pin on the opposite side of the ball has one end exposed to discharge pressure. The bias pin and the stem of the bellows cooperate depending upon the discharge and intake pressure to vary the control pressure at one side of the actuator for moving the rotary valve plate.
Normally, the suction pressure set point for the bellows must be adjusted for each control valve during assembly. The suction pressure set point is the point at which the suction pressure is sufficiently low relative to the discharge pressure to cause the stem of the bellows to move the ball off of the seat. In one type of compressor being manufactured, this is handled by installing the components of the control valve in the compressor, completing the assembly of the compressor, and operating the compressor with nitrogen. The operator monitors pressures and adjusts the suction pressure set point with an adjustment screw that contacts one end of the bellows. This procedure is time consuming and expensive.